$ { {4} \times \left[\begin{array}{rr}{2} & {-1} \\ {-1} & {-1}\end{array}\right] = {?} } $
To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{4}\times{2} & {4}\times{-1} \\ {4}\times{-1} & {4}\times{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{8} & {-4} \\ {-4} & {-4}\end{array}\right]}$